Targeting the EphB4 receptor tyrosine kinase sensitizes HER2-positive breast cancer cells to Lapatinib.

Clinical data analysis reveals that the expression of the EphB4 receptor tyrosine kinase is significantly elevated in HER2-positive breast cancer and high levels of EphB4 strongly correlate with poor disease prognosis. However, the impact of EphB4 activation on HER2-positive breast cancer cells and the potential of EphB4 as a therapeutic target remain to be explored. Here, we show that EphB4 overexpression confers gain-of-function activities to HER2-positive breast cancer cells, rendering resistance to a HER2/EGFR inhibitor Lapatinib. Furthermore, using integrated transcriptomic and tyrosine phosphoproteomic analyses, followed by biochemical confirmation, we establish that EphB4 activation engages the SHP2/GAB1-MEK signaling cascade and downstream c-MYC activation, and thereby limits the overall drug responses to Lapatinib. Finally, we demonstrate that, in HER2-positive breast tumors, inhibition of EphB4 combined with Lapatinib is more effective than either alone. These findings provide new insights into the signaling networks dictating therapeutic response to Lapatinib as well as a rationale for co-targeting EphB4 in HER2-positive breast cancer.

MYC status as a determinant of synergistic response to Olaparib and Palbociclib in ovarian cancer.

BACKGROUND: While PARP inhibitors and CDK4/6 inhibitors, the two classes of FDA-approved agents, have shown promising clinical benefits, there is an urgent need to develop new therapeutic strategies to improve clinical response. Meanwhile, extending the utility of these inhibitors beyond their respective molecularly defined cancer types is challenging and will likely require biomarkers predictive of treatment response especially when used in a combination drug development setting. METHODS: The effects of PARP inhibitor Olaparib and CDK4/6 inhibitor Palbociclib on ovarian cancer cells lines including those of high-grade serous histology were examined in vitro and in vivo. We investigated the molecular mechanism underlying the synergistic effects of drug combination. FINDINGS: We show for the first time that combining PARP and CDK4/6 inhibition has synergistic effects against MYC overexpressing ovarian cancer cells both in vitro and in vivo. Mechanistically, we find that Palbociclib induces homologous recombination (HR) deficiency through downregulation of MYC-regulated HR pathway genes, causing synthetic lethality with Olaparib. We further demonstrate that MYC expression determines sensitivity to combinatorial treatment with Olaparib and Palbociclib. INTERPRETATION: Our data provide a rationale for clinical evaluation of therapeutic synergy of these two classes of inhibitors in ovarian cancer patients whose tumors show high MYC expression and who do not respond to PARP inhibitors or CDK4/6 inhibitors monotherapies. FUND: This work was supported by the National Natural Science Foundation of China [81672575, 81874111, 81472447 to HC; 81572586 and 81372853 to PL], and the Liaoning Provincial Key Basic Research Program for Universities [LZ2017002 to HC].

Targeting P16INK4A in uterine serous carcinoma through inhibition of histone demethylation.

Uterine serous carcinoma (USC) is a subtype of endometrial cancer. Compared with endometrial endometroid carcinoma, the majority of USC cases are more aggressive. Cyclin-dependent kinase inhibitor 2A (P16INK4A) is a canonical tumor suppressor that blocks cell cycle progression; however, P16INK4A is overexpressed in USC. The aim of the present study was to determine the role of P16INK4A in P16INK4A­positive endometrial cancer, with the hope of elucidating a novel therapeutic approach for this type of malignancy. A total of 2 endometrial cancer cell lines, ETN­1 and EFE­184, were selected for further investigation, due to them being known to express high levels of P16INK4A. Using short hairpin RNA targeting P16INK4A, P16INK4A was downregulated in these cancer cell lines. Cell viability and migration were examined via 2D/3D clonogenic and wound healing assays. Subsequently, GSK­J4, a histone demethylase inhibitor, was employed to deplete P16INK4A in these cancer cell lines and an ex vivo culture system of a patient­derived xenograft (PDX) endometrial tumor sample. Following P16INK4A knockdown, the proliferation and migration of ETN­1 and EFE­184 cells markedly declined. When exposed to GSK­J4, the levels of KDM6B and P16INK4A were almost completely abrogated, and the cell viability was significantly reduced in these cell lines and the ex vivo­cultured PDX tumor explants. The association between the levels of P16INK4A, lysine demethylase 6B (KDM6B) and the methylation status of histone 3 lysine 27 (H3K27) in these cell lines and the human USC tumor sample was also demonstrated. P16INK4A appears to be oncogenic in a number of endometrial cancer cell lines. The level of P16INK4A is associated with the methylation status of H3K27. Increased methylation of H3K27 coexists with downregulation of KDM6B and, subsequently, P16INK4A, which reduces cell proliferation and invasiveness in endometrial cancer. The observations of the present study may enable the development of a novel therapeutic strategy for P16INK4A­positive endometrial cancer, particularly USC.

Inhibition of BTF3 sensitizes luminal breast cancer cells to PI3Kα inhibition through the transcriptional regulation of ERα.

Selective phosphatidylinositol 3 kinase (PI3K) inhibitors are being actively tested in clinical trials for ERα-positive (ER+) breast cancer due to the presence of activating PIK3CA mutations. However, recent studies have revealed that increased ERα transcriptional activity limits the efficacy of PI3K inhibitor monotherapy for ER + breast cancers. Herein, we report the identification of BTF3 as an oncogenic transcription factor that regulates ERα expression in luminal breast cancers. Our TCGA analysis reveals high expression levels of BTF3 in luminal/ER + breast cancer and cell line models harboring ERα overexpression. Concordantly, BTF3 expression is highly and strongly associated with ESR1 expression in multiple breast cancer cohorts. We further show that BTF3 promotes the proliferation, survival and migration of ER + breast cancer cells by modulating ESR1 expression and ERα-dependent transcription. Moreover, BTF3 knockdown sensitizes ER + breast cancer cells to the PI3Kα inhibitor BYL-719 in both in vitro and in vivo models. Together, our findings highlight a novel role of BTF3 in modulation of ERα-dependent transcriptional activity and its potential as a predictive marker for the response to PI3K-targeted therapy in ER + breast cancer.